Elevator Controller SCCR

[JoesBagelandDeli]

A couple of weeks ago, I reached out to the architect and requested that they update their elevator spec to identify a minimum SCCR of 35kA. They then sent that revised spec to their elevator vendors. The most positive response we received was that it'll cost a significant amount of money while others simply said they can't do it.

I feel as though I have two options at this point if the best SCCR for an elevator controller we can assume is 10kA.

Option 1:
Feed this off the 208V distribution where the available FC falls below 10kA.
Downside: Larger breaker and conductors, and will likely push low-voltage transformer into next size up= more money

Option 2:
Feed this off of the 480V distribution where the available FC at the elevator is ~32kA.
Provide a fused disconnect with current limiting fuses, and direct the elevator manf. to not include an OCPD within their controller and/or disconnecting means.

Downside: The use of CLFs appears to be a contentious topic on this forum and elsewhere. Many people whose opinions i respect on this forum seem to not be willing to sign off on their use - per 240.86(A).

Are there other options or considerations?

 

[synchro]

Use a dedicated transformer to feed the elevator in order to limit the available fault current to the desired value?

 

[jim dungar]

Option 2 is valid only if the elevator controls and fuses have been tested and listed as a combination. It makes no difference if they have an integral OCP or not.

Fuses do not really lower the fault current until the fault current reaches their current limiting threshold.

 

[JoesBagelandDeli]

Option 2 is valid only if the elevator controls and fuses have been tested and listed as a combination. It makes no difference if they have an integral OCP or not.

Fuses do not really lower the fault current until the fault current reaches their current limiting threshold.

Are you saying series combinations include controllers and not just OCPDs?

 

[augie47]

We can assume you took the feeder length and conductor size into account

 

[ron]

We force the elevator vendor to provide the correctly rated short circuit current for their controller. We do the same for all the HVAC guys too.

 

[petersonra]

I can't imagine what would be in an elevator controller that would require a whole lot to increase the SCCR to something respectable.

OTOH, it does not take a lot of smallish wire to cut the ASCC down to a reasonable level either.

 

[JoesBagelandDeli]

We force the elevator vendor to provide the correctly rated short circuit current for their controller. We do the same for all the HVAC guys too.

The HVAC equipment suppliers seem much more familiar with all of this and much more willing to accommodate the higher SCCR if needed.
On the topic of HVAC equipment. For a typical new commercial bldg with unit heaters, fans, water heaters, water softeners, pumps, chillers, AHUs, VRF units, etc etc. Are you confirming the available fault current at all of those pieces of equipment, and then coordinating that information with the appropriate engineer for them to then pass that on to their supplier? From my experience, it seems most people focus on the larger pieces of equipment such as chillers, RTUs, and AHUs.

 

[petersonra]

The thing is that most of the time it does not matter much what brands of equipment you are using. It is not real hard to get to 65ka SCCR. And very few places you would apply package elevator equipment or HVAC equipment would be above that level of SCC.

 

[ron]

The HVAC equipment suppliers seem much more familiar with all of this and much more willing to accommodate the higher SCCR if needed.
On the topic of HVAC equipment. For a typical new commercial bldg with unit heaters, fans, water heaters, water softeners, pumps, chillers, AHUs, VRF units, etc etc. Are you confirming the available fault current at all of those pieces of equipment, and then coordinating that information with the appropriate engineer for them to then pass that on to their supplier? From my experience, it seems most people focus on the larger pieces of equipment such as chillers, RTUs, and AHUs.

We are not as complete as I would like, but I try to coordinate with all of that equipment when I remember.

 

[augie47]

What is the actual current available at the end of your feeder ??

 

[topgone]

What is the actual current available at the end of your feeder ??

To help the poster, we need to ask where does his feeder come from? A distribution transformer on poles? Or a pad-mounted transformer vault? What size is the transformer? What size of conductors were used from the rtansformer/s? How long is his feeder from the source transformer?
It would be easier for the poster to start his calculations of the available fault on his end of the feeder (fault occurring at feeder's end), IMO (using the infinite impedance of the system).

 

[Jraef]

The thing is that most of the time it does not matter much what brands of equipment you are using. It is not real hard to get to 65ka SCCR. And very few places you would apply package elevator equipment or HVAC equipment would be above that level of SCC.

This is correct, it is not at all difficult to attain a decent SCCR value. That is, unless they are ignorant of the process and unwilling to learn, or they are so committed to using only the cheapest components that are not series listed that they cannot see the value to their customers in complying.

For example if you want a motor starter listed at a higher SCCR when protected by a circuit breaker (instead of fuses), then it’s a given that you must use a starter from the same manufacturer as the breaker, because one mfr is not going to spend the money to series test with a competitor. That’s really all it takes now, but it means if the correct breaker is $5 more than the one you have been using, it cuts your profits or increases your sell prices and THAT is what some OEMs object to.

 

[Strathead]

This is correct, it is not at all difficult to attain a decent SCCR value. That is, unless they are ignorant of the process and unwilling to learn, or they are so committed to using only the cheapest components that are not series listed that they cannot see the value to their customers in complying.

For example if you want a motor starter listed at a higher SCCR when protected by a circuit breaker (instead of fuses), then it’s a given that you must use a starter from the same manufacturer as the breaker, because one mfr is not going to spend the money to series test with a competitor. That’s really all it takes now, but it means if the correct breaker is $5 more than the one you have been using, it cuts your profits or increases your sell prices and THAT is what some OEMs object to.

That is all well and good for a starter, but it doesn't make the equipment itself easy to get a higher SCR. The elevators I have worked on recently require us to confirm an SCR of 5,000 maximum. It was accepted that current limiting fuses would be acceptable. A 400 amp J type fuse has a let through of just less than 5000 amps, so why is there a discussion that it wouldn't be adequate to reduce the current to an SCCR of 5,000?

 

[augie47]

"It was accepted that current limiting fuses would be acceptable."
At one time that was the case here and in many other installations but 110.22 & 240.86 require the method of reduction must be thru a LISTED combination or designed by a professional engineer. We can no longer look at "let thru current" and use that as documentation.
Others here, far more learned than I, can explain the "why:.

 

[ron]

"It was accepted that current limiting fuses would be acceptable."
At one time that was the case here and in many other installations but 110.22 & 240.86 require the method of reduction must be thru a LISTED combination or designed by a professional engineer. We can no longer look at "let thru current" and use that as documentation.
Others here, far more learned than I, can explain the "why:.

Augie is right on target. Dynamic impedance is the reason.

Even if it was an existing condition allowing 240.86(A), and you could find a PE willing to stamp it (most will not), it clearly says that the downstream needs to be passive during the interrupting process, so no contactors or other OCPDs.

For new installations, it needs to be a tested combination.

 

[jim dungar]

For new installations, it needs to be a tested combination.

This has been true for several decades now.

 

[JoesBagelandDeli]

Augie is right on target. Dynamic impedance is the reason.

Even if it was an existing condition allowing 240.86(A), and you could find a PE willing to stamp it (most will not), it clearly says that the downstream needs to be passive during the interrupting process, so no contactors or other OCPDs.

For new installations, it needs to be a tested combination.

Would it work to provide a fused disconnect with RK fuses and not have OCP within the equipment's controller? There would be no dynamic impedance with respect to the controller and fuse combination, right? But would you then have to evaluate the dynamic impedance between the branch circuit breaker upstream of the fused disconnect in combination with the fused disconnect?

 

[JoesBagelandDeli]

To help the poster, we need to ask where does his feeder come from? A distribution transformer on poles? Or a pad-mounted transformer vault? What size is the transformer? What size of conductors were used from the rtansformer/s? How long is his feeder from the source transformer?
It would be easier for the poster to start his calculations of the available fault on his end of the feeder (fault occurring at feeder's end), IMO (using the infinite impedance of the system).

These are branch panelboards that'll be used to feed the elevator and are well downstream of the service entrance. You'll just have to take my word for it that the fault current numbers I've given are accurate or we can assume this is an academic exercise - which I'm also okay with.

 

[jim dungar]

Would it work to provide a fused disconnect with RK fuses and not have OCP within the equipment's controller?

No.
Especially if the controller contains components like contactors, relays, or VFD.